1. Field of the Invention
The present invention relates to an organic light emitting device (OLED) and a method of manufacturing the same, and more particularly, to a polymer OLED that uses a self-buffer layer to improve color purity and improve lifespan.
2. Description of the Related Art
OLEDs are self-light-emitting type light emitting display devices that emit light using an organic compound. OLEDs are thin and have higher response speed, lower power consumption, and lower manufacturing costs than TFT-LCDs since they have a simpler structure and a simpler manufacturing process.
OLEDs are devices that transform electrical energy into optical energy in an organic material. That is, the OLEDs are devices that emit light by generating excitons by recombining holes and electrons respectively injected from an anode and a cathode into the organic material.
A basic structure of a conventional OLED includes an anode, an emission material layer, a cathode that are sequentially stacked. The performance of the OLED is largely affected by the variation of a multi-layer thin film structure, and the light emitting efficiency and lifespan of the OLED can be improved by adding various functional layers to the basic structure.
Conventional OLEDs can be manufactured by organic molecular beam deposition (OMBD), i.e., a dry process, but polymer OLEDs are mainly manufactured by a spin coating method or an ink jet method, i.e., wet processes, to form multi-layer thin films.
The conventional OLED includes a transparent electrode, a hole injection layer, a hole transport layer, a light emitting layer, and an upper electrode sequentially stacked on a transparent substrate. Multi-layer thin films are included in the conventional OLED and the lifespan of the device can be improved by complementary functions of each of the multi-layer thin films.
Meanwhile, a spin coating method is generally used for forming the light emitting layer on the hole transport layer when the conventional OLED is manufactured. However, a solution used for the spin coating method can dissolve the hole injection layer and a hole transport layer, which are lower layers, since the solution contains a solvent such as chlorobenzene, toluene, xylene, cyclohexanone, chloroform, or THF, which has high solubility with a main component of the light emitting layer.
That is, an already stacked layer can be dissolved since a solution used for a wet process for forming a multi-layer thin film generally contains a solvent having high solubility. Defects generated at this time can reduce the lifespan and color purity of a device. However, if a solvent having low solubility is used, each layer can not be formed to a desired thickness. What is therefore needed is an improved OLED and a method of making the same where the underlying layers do not have many defects while allowing for subsequent layers to be formed at an adequate thickness.